A decade of the rosary is a grouping of prayers that consists of one "Our Father" followed by ten "Hail Mary" prayers. While reciting the ten Hail Mary prayers, one must also meditate on one of the Mysteries of the Rosary. It is the added meditation which makes "decade" different than ordinary prayer.

There are twenty decades in a full Rosary, and it is common practice to recite five decades a day while meditating on the Rosary Mysteries assigned to that given day.